1. Field of This Invention
This invention relates to apparatus for atomizing liquids. This invention more particularly relates to apparatus for atomizing liquids which substantially comprises an ultrasonic excitation system, a bending resonator which oscillates at ultrasonic frequencies, and means for the delivery of liquid into the velocity nodal region of the bending resonator.
2. Prior Art
In conventional ultrasonic capillary wave atomizers, the fine dispersion effect is produced by cutting off drops from a stationary capillary wave grid with nodal lines which are arranged in a chessboard-like manner--the grid being formed on a thin film of liquid which is excited by the surface of an oscillating solid body. The atomization effect requires an excitation amplitude, which is dependent on the frequency and various parameters of the liquid, in respect of the oscillating solid body surface, and a suitable thickness of the film of liquid. If the film is excessively thin, drops cannot be formed; while if the film is excessively thick, damping prevents effective capillary waves from being stimulated in the liquid.
In order to achieve the optimum specific atomization through-put in relation to surface area (of a few liters per hour and cm.sup.2) with low-viscosity liquids, the liquid must be continuously fed onto the atomizer surface in such a way as to maintain the optimum possible thickness of film over the maximum area of the oscillating surface.
With the conventional mode of supplying the liquid through an axial bore in the ultrasonic atomizer, the required manner of operation can be achieved only up to relatively low levels of through-put of less than 5 liters per hour. However, when an internal liquid supply arrangement of such kind is used, cavitation sputtering occurs, particularly at higher rates of through-put. Cavitation sputtering results in unacceptable impairment of the drop spectrum. Such effect can be prevented by using an external liquid supply arrangement involving a plurality of pipes. Such a construction may be uneconomical and may not be the optimum arrangement under some circumstances, at high rates of through-put. Added to this is the fact that the known apparatuses do not make it possible to effect separation into different particle sizes, for example, when producing powder.